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Date: Sun, 17 Dec 2006 03:45:13 +1100 (EST)
From: Allen Patterson Hazen <allenph@unimelb.edu.au>
Subject: Re: Mesozoic gliding mammal
To: dinosaur@usc.edu
As I read the paper, the current count is that the general morphology of a
gliding patagium stretched between the fore and hind legs and with no
internal skeletal support has evolved at least nine separate times in
various mammal(-iform) lineages: the new beastie, the presumed but so-far
undiscovered ancestor of bats, and seven others. (Extant flying
"squirrels" are apparently not a single lineage; ditto for Australian
marsupial gliders. The 30-million year old rodent mentioned is, if I
recall correctly, more closely related to dormice (dormouses?) than to
flying squirrels. And at least the latest molecular stuff I've seen
suggests that flying lemurs are NOT closely related to bats-- colugos
apparently close to primates, bats closer to carnivores and pangolins and
perissodactyls.)
Note that no mammal has ever (as far as known) evolved a morphology
resembling the extant Draco volans or the two (?) extinct suropsids
(Kueneosaurus? and ???) that superficially resembled it.
Without going off the typological or orthogenetic deep end, doesn't this
suggest that the mammalian Bauplan predisposes mammals to evolve one sort
of gliding morphology and very strongly predisposes them NOT to evolve
another? At a guess, the involvement of the mammalian rib-cage in
resperation makes it at least very difficult to develope something
Draco-like, with gliding surface supported by rib extensions.
---
Allen Hazen
Philosophy Department
University of Melbourne
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